1. Technical Field of the Invention
This invention relates to a piston ring and cylinder liner combination for internal combustion engines.
2. Description of the Related Art
In recent years demands have been made for stronger cylinder liners to match high engine output. To meet these demands, a composite cylinder liner comprising an inner layer of special cast iron with superior wear resistance and scuffing resistance and an outer layer of graphite steel with superior toughness was proposed in Japanese Patent Publication No. 5-38061. Further, in Japanese Laid-Open Patent No. 7-164131, spheroidal graphite cast iron material with superior toughness was utilized in the cylinder block and the method which prevents a decrease in wear resistance, in other words, the phenomenon that the periphery of the spheroidal graphite is covered by means of the plastic deformation of the base material by hardening the base material of the sliding portions was proposed.
However, the piston ring operating environment has become much harsher due to high engine output, making the use of treatment technologies such as physical vapor deposition processing or chemical vapor deposition processing on the outer circumference of the ring. These methods are referred as plating in a dry process or reactive vapor deposition and serve to maintain high wear resistance and high scuffing resistance.
The composite chromium plating film is known as a hard film treatment in a wet process and provides high wear resistance and scuffing resistance equivalent to the hard film formed by physical vapor deposition processing or chemical vapor deposition processing.
In the above-mentioned liner and block technologies, the liner and block were made of high grade cast iron, and improvements and improved surface for the liner and block were adopted as countermeasures to the disadvantage of the high grade cast iron material, namely that sliding characteristics were weaker than gray cast iron material.
In the above-mentioned piston ring technology, there were no particular specifications for the material of the cylinder liner. However, the embodiments of engine tests using the gray cast iron liner and resultant explanations suggest that a mating material is gray cast iron material which provides superior wear resistance and scuffing resistance.